Current American Heart Association guidelines call for chest compressions during cardio-pulmonary resuscitation (CPR) to be performed at a rate of 80 to 100 per minute and at a depth of 1.5 inches to 2.0 inches. (Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, 102 Circulation Supp. I (2000).) When a first aid provider performs CPR according to these guidelines, blood flow in the body is about 25 to 30% of normal. However, when chest compressions are required for long periods of time it is difficult, if not impossible, to maintain adequate compression of the heart and rib cage. Even experienced paramedics cannot maintain adequate chest compressions for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, long periods of CPR, when required, are often not successful at sustaining or reviving the patient. At the same time, it appears that if chest compressions could be adequately maintained then cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended CPR efforts (45 to 90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
In efforts to provide better blood flow and increase the effectiveness of resuscitation efforts, we have developed a chest compression system which automatically compresses the chest of a heart attack victim. The device includes a broad belt that wraps around the chest of the patient. The belt is repeatedly tightened around the chest to cause the chest compressions necessary for CPR. Our devices are described in co-pending application Ser. No. 09/866,377 filed May 21, 2001 and Ser. No. 09/087,29 filed May 29, 1998, the entire disclosures of which are hereby incorporated by reference. Other modifications of the basic CPR procedure have been proposed. Woudenberg, Cardiopulmonary Resuscitator, U.S. Pat. No. 4,664,098 (May 12, 1987) shows such a chest compression device that is powered with an air cylinder. Waide, et al., External Cardiac Massage Device, U.S. Pat. No. 5,399,148 (Mar. 21, 1995) shows another such device which is manually operated. Lach, et al., Resuscitation Method and Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13, 1988), proposed compression of the chest with wide band and chocks on either side of the back, applying a side-to-side clasping action on the chest to compress the chest. Kelly et al., Chest Compression Apparatus for Cardiac Arrest, U.S. Pat. No. 5,738,637 (Apr. 14, 1998) uses a flexible, inelastic belt attached to a scissors-like means for compressing the chest. Inflatable vests are also proposed for compressing the chest for CPR, as shown in Halperin, Cardiopulmonary Resuscitation and Assisted Circulation System, U.S. Pat. No. 4,928,674 (May 29, 1990). The commercially available Thumper device, shown in Barkolow, Cardiopulmonary Resuscitator Massager Pad, U.S. Pat. No. 4,570,615 (Feb. 18, 1986) and other such devices, provides continuous automatic closed chest compression. Barkolow provides a piston which is placed over the chest cavity and supported by an arrangement of beams. The piston is placed over the sternum of a patient and set to repeatedly push downward on the chest under pneumatic power.